The present invention relates to a ferromagnetic material having a wide range of application in technical fields, and magnetic apparatuses including high-density magnetic recording apparatuses and magnetic sensors and employing such a ferromagnetic material.
A ferromagnetic material is a substance having spontaneous magnetization, i.e., a substance having a finite magnetization intensity. Sometimes, a ferromagnetic material in bulk does not display any finite magnetization intensity. In such a state, the interior of the ferromagnetic material is divided into a plurality of regions, each of the regions displays magnetization of a finite intensity, and the directions of magnetization of the regions are different from each other. A small region in which spontaneous magnetization has a fixed direction is called a magnetic domain.
A ferromagnetic material is applied widely to various magnetic devices including various magnetic recording systems and magnetic sensors. Efforts have been made for the development of various ferromagnetic materials suitable for different purposes. In the field of magnetic recording, in particular, the reduction in size of magnetic domains and the realization of recording of a minimum unit by a smallest possible number of magnetic domains are important problems. Although a plurality of magnetic domains serve as a recording unit in current magnetic recording, it is desirable to use a single magnetic domain as a recording unit when all is said and done, and it is desirable to reduce the size of magnetic domains each for a recording unit.
A method of making a ferromagnetic material having small magnetic domains employing electron beam lithography is disclosed in, for example, Journal of Applied Physics, Vol. 76, pp. 6673-6675 (1994). This method forms a region of several tens nanometer square of magnetic atoms on a nonmagnetic substrate, i.e., a material not displaying ferromagnetism. It is reported in this paper that the region displays ferromagnetism in a single magnetic domain in some cases. Magnetic atoms are atoms which display ferromagnetism in single bulk, such as those of 3d transition metals including Cr, Mn, Fe, Co and Ni, and lanthanides including Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er and Tm.
A region of a ferromagnetic material of a size on the order of the foregoing size can be formed by depositing the ferromagnetic material on a nonmagnetic substrate with the probe of a scanning tunneling microscope (STM) as mentioned in, for example, Journal of Applied Physics, Vol. 76, pp. 6656-6660 (1994).